Interferometry is a useful technique for measuring one or more spatial characteristics of a sample, such as a semiconductor wafer or any other semiconductor or non-semiconductor substrate, based on information associated with illumination reflected from test surfaces of the sample. As semiconductor fabrication continually requires higher levels of accuracy and precision, improved interferometry techniques are needed to meet the demands of modern fabrication technologies. Measurements of the absolute thickness distribution t(x,y) of a wafer or a thin film is often desired. Currently, the measurement of the absolute thickness distribution t(x,y) of a bare wafer is accomplished through the combination of dual interferometry measurements and capacitance gauge (CG) or optical thickness gauge (OTG) measurements, which are performed across the wafer. CG measurements involve the use of capacitive displacement sensors, which can only be used to measure substrates that can be virtually grounded. OTG measurements involve the use of laser displacement sensors and can only sense a material surface if it is reflective of the incident laser beam. Both of these approaches suffer from significant limitations. Therefore, it is desirable to provide a system and method that overcomes the shortfalls of the previous approaches discussed above.